1. Field of the Invention
This invention relates to an abrasive tape to be used for polishing of a magnetic head or the like. This invention particularly relates to an abrasive tape to be used for finish polishing of a rough-polished surface of a magnetic head or the like.
2. Description of the Prior Art
Video or high-grade audio magnetic heads are made by being polished with abrasive tapes. The abrasive tape comprises a flexible substrate, and an abrasive layer overlaid on the flexible substrate. In order to provide the abrasive layer, an abrasive composition consisting of abrasive grains, a binder, additives and the like is applied onto the flexible substrate and dried.
In general, when the surface of a magnetic head or the like is to be polished with the abrasive tape, two reels are positioned with the magnetic head or the like intervening therebetween, and the abrasive tape is moved in contact with the surface to be polished between two reels. The abrasive tape is flexible and can snugly fit to a curved surface. Therefore, the abrasive tape is more suitable for the polishing of the curved surface of the magnetic head or the like than grinding wheels. Also, the abrasive tape can achieve scratch-free, accurate polishing of the surface to be polished, and is therefore indispensable to finish polishing of a rough-polished surface.
As is well known, polishing processes wherein the abrasive tape is used are carried out for the purposes of shaping the tip of a magnetic head into a desired form, eliminating the chipping of a magnetic head, and polishing the surface of a magnetic head to a smooth finish. In order to achieve the polishing process in good manner, it is required that the polishing performance be increased, thereby to shorten the time required for the polishing, and that the smoothness of the polished surface be increased. In order to increase the polishing performance, an abrasive tape provided with hard, large-sized abrasive grains may be used. However, when the abrasive tape provided with hard, large-sized abrasive grains is used, the smoothness of the polished surface cannot be increased. On the contrary, in order to increase the smoothness of the polished surface, an abrasive tape provided with soft, small-sized abrasive grains may be used. However, the polishing performance of the abrasive tape provided with soft, small-sized abrasive grains is low. Therefore, various attempts have been made to provide an abrasive tape which would satisfy both the two incompatible requirements described above. For example, it has been proposed in Japanese Unexamined Patent Publication No. 54(1979)-97408 to employ two types of abrasive grains as the abrasive grains contained in the abrasive layer of an abrasive tape, thereby to increase both the polishing performance of the abrasive tape and the smoothness of a polished surface.
In recent years, information is recorded at an increasingly higher density on magnetic recording media such as video tapes, and therefore magnetic heads are required to exhibit more excellent characteristics. For example, the shortest recording wavelength was approximately 1 .mu.m for conventional video tapes, and is as short as 0.8 .mu.m for the S-VHS system video tapes (such as S-MASTER supplied by Fuji Photo Film Co., Ltd. and 5516XTS supplied by Sumitomo 3M Ltd.). As the recording wavelengths are shortened, it is required to improve the characteristics of the magnetic heads. However, the abrasive tape proposed in, for example, Japanese Unexamined Patent Publication No. 54(1979)-97408 is designed to polish magnetic heads to be used with recording wavelengths of approximately 1 .mu.m, and is not suitable for the polishing of magnetic heads which are recently required to exhibit more excellent characteristics.